MOUNT PLEASANT, Iowa, Dec. 26 -- With just eight days left to break a three-way deadlock in the Democratic contest here, Sen. Hillary Rodham Clinton began delivering a closing argument Wednesday that centered on the experience she and her husband gained in the Oval Office during his administration, while her two chief rivals both argued that they could best succeed in bringing change to Washington.

The issues of experience and change have defined the Democratic race for nearly a year, and the dichotomy continued to dominate as the three Democratic front-runners hit the campaign trail running after a Christmas break. Sen. Barack Obama (Ill.), who plans to make his endgame pitch in a speech on Thursday, urged voters to ask themselves, "Do you believe in change?" Former senator John Edwards (N.C.) detoured through New Hampshire before a planned return to Iowa, arguing that his is a more radical call for change than Obama's. Clinton and Obama are launching television ads in the state to bolster their arguments as the three remain tightly bunched in surveys.

Clinton, campaigning with her husband and daughter on a tour themed "It's Time to Pick a President," injected a note of menace into her case, arguing that "the job itself is unpredictable" and that only she among the candidates is qualified to do it.

"You never know what may happen in some part of the world that will create a real challenge to us here at home, here in Iowa," Clinton told a packed auditorium Wednesday.

Polls show that experience has been the attribute on which Clinton (N.Y.) has enjoyed the biggest advantage over Edwards and Obama, and she has sought to pound that theme on the stump. But her competitors have argued that she has the wrong kind of experience to bring change to the White House, a subtle means of referencing some of the knottier chapters of the Clinton administration, and sought to turn a potential asset into a liability for her.

Clinton has shifted from theme to theme in the final weeks of a race that has remained consistently up for grabs, but she seemed to settle back on her original experience argument after two months of attempting to show voters a softer side. Yesterday she criticized Obama's character and questioned whether other Democratic contenders are equipped to beat the eventual Republican nominee. Bill Clinton, introducing his wife, promised that "if she is the Democratic nominee, I believe she will win the election, and win by a handsome margin." In addition to the former president, who is scheduled to continue acting as a surrogate for his wife over the next few days, a team of "Hill's Angels" that includes fundraiser Terence R. McAuliffe and women's outreach organizer Ann Lewis is planning to fan out on Clinton's behalf across the state. Iowans, who continue to deal with treacherous conditions and temperatures struggling to stay about freezing, are now also weathering a blizzard of campaign advertisements, political appearances and attention from news outlets worldwide.

Obama will use his speech on Thursday morning in Des Moines to frame his case to Iowa voters, but as he rolled through north-central part of the state Wednesday he offered a preview, pleading with voters to have the courage to vote their hopes and not their fears. "If you believe I can be the next president of the United States, it can happen," he told an overflow crowd in Webster City.

The senator from Illinois directly addressed doubts that voters may have about him and warned that, in the final days in Iowa, his opponents are likely to seek to exploit them even more. "People start running negative ads or negative mail, and they start planting seeds of doubt. They say 'Oh, you know, Obama is young' or 'You know, is he electable enough?' "

Obama exhorted his audiences to put their faith in their own instincts. "The question is, do you believe in change?" he said. "The question is do you believe deep in your gut that we can do better than we're doing? You know we can, and you have to trust that sense that we can do better because every generation is tested in this way and this is our moment to try to break out of the conventional wisdom and get something done."

Clinton officials sought to cast Obama's remarks as "negative attacks," adding to an atmosphere of heightening hostility in the final days before voting begins in a state that has historically rejected negative campaigning in the Democratic field.

David Axelrod, Obama's chief strategist, said that Obama's speech Thursday will not attempt to reinvent the candidate's message but that "we're getting down to the jury deliberation here" and it is essential for all the candidates to sharpen their closing arguments.

"We really believe this is an election about change and that he is the authentic exponent of change," Axelrod said. "He's the candidate who will bring it. That's the premise on which this candidacy was predicated, and now's the time to close the circle on that message and leave it to people to make that decision."

Axelrod said addressing doubts about the candidate is an essential part of spurring voters to support Obama on Jan. 3. "There's always a mixed impulse" on the part of the voters, he said. "There's an impulse to sort of stick with the known rather than taking a chance on change. It's the same force, as he noted, that Bill Clinton confronted in 1992 . . . We have to urge people to fight their way through it and make a reasoned judgment based on what they've seen and heard." Edwards spent the day campaigning in New Hampshire, which one adviser called a sign of the candidate's growing confidence that he is in a strong position in Iowa and determined not to repeat his mistake of four years ago, when he put too little effort into the Granite State and finished poorly after a strong second-place showing in Iowa.

His campaign issued a strategy memo from his deputy campaign manager, Jonathan Prince, arguing that the former senator has gained momentum in Iowa over the past 10 days and that he will close out his campaigning in Iowa emphasizing kitchen-table issues and a more radical call for change than Obama's. "We know the message is resonating with Iowa voters," Prince said in the memo.

Another senior adviser said Edwards's core message will include the assertion that what is needed in Washington is a fighter who will take on special interests, not negotiate with them. The aide said Edwards believes it is essential in the final days to make certain voters understand the differences among the candidates -- "to make it very clear what an Edwards presidency will be about and how it would differ from Clinton and Obama."